In electronic display technology, four-digit digital displays are a common display device, widely used in various digital display systems. They display numbers or characters by controlling different segments of light-emitting diodes (LEDs) (A-G). For a four-digit digital display with 12 pins, proper pin assignment is crucial for achieving stable display functionality and efficient circuit design. This article will delve into the principles and specific pin assignments for the 12 pins of a four-digit digital display, as well as practical considerations for practical applications.

I. Basic Structure and Operating Principle of a Four-Digit Digital Display
A four-digit digital display consists of four independent seven-segment LED displays. Each display contains seven LED segments (A, B, C, D, E, F, G) and an optional decimal point (DP). These segments connect to external circuitry via specific pins. By controlling the voltage levels of these pins, the corresponding LED segments can be illuminated or extinguished, thereby displaying the desired number or character.

II. Principles of 12-Pin Assignment
Common Anode vs. Common Cathode: The pin assignment of a four-digit digital display first requires consideration of whether it is a common anode or common cathode type. The anode (positive) of a common anode digital tube is connected together, while the cathode (negative) of each segment is connected separately. Common cathode digital tubes have the opposite behavior: the cathodes are connected together, and the anodes are connected separately.

Segment Select and Bit Select: To achieve multi-digit display, both segment select (controlling which digit or character is displayed) and bit select (selecting which digit to display) are required. Therefore, the pin assignment must clearly distinguish between segment select and bit select pins.

Pin Number and Function: A 4-digit digital tube with 12 pins typically includes 8 segment select pins (A-G and DP) and 4 bit select pins (used to select which digit to display).

III. Specific Allocation of the 12 Pins
Segment Select Pins: Pins A, B, C, D, E, F, and G correspond to the seven LED segments of the digital tube and are used to control the displayed digit or character. Pin DP is the decimal point pin, used to display the decimal point.

Bit Select Pins: Four pins (such as D1, D2, D3, and D4) are typically used as bit select pins to select which digital display to display. By controlling the voltage levels of these four pins, each digit in the four-digit display can be illuminated sequentially.

IV. Pin Assignment Notes
Pin Identification and Connection: In actual applications, carefully check the pin identification of the digital display to ensure the correct connection of the segment select pins and bit select pins. Incorrect connection may cause display abnormalities or damage the digital display.

Current Limiting Resistor: To protect the LED segments from overcurrent damage, a current limiting resistor is typically connected in series between the segment select pins and the driver circuit. The value of the current limiting resistor should be determined based on the rated voltage and current of the LED and the power supply voltage.

Driver Circuit: Select an appropriate driver circuit based on the digital display type (common anode or common cathode) and display requirements. The driver circuit should be able to provide sufficient current to illuminate the LED segments and have good stability and reliability.

Display Mode: The four-digit digital display can display in either static or dynamic mode. During static display, all bits are lit at the same time; during dynamic display, each digital tube is lit in turn by quickly switching the state of the bit select pin, and the visual persistence effect of the human eye is used to achieve the effect of simultaneous display of multiple bits.